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COAL UTILIZATION IN THE STEEL INDUSTRY

The largest single use of coal in the steel industry is as a fuel for the blast furnace, either for the production of metallurgical coke or for injection with the hot blast. Other less commonly thought of uses of coal is for making steam and electricity, as sources of carbon addition in steel making processes, and in direct smelting of iron processes. Furthermore, electricity purchased from outside sources is largely generated from pulverized coal combustion and therefore has an indirect influence on steel making operations. Except for coke making, the requirements for a quality coal product are fairly simple. For pulverized coal combustion, whether taking place in a combustion unit or in the blast furnace, the coal must deliver a known and consistent calorific value, be reasonably low in ash yield or have relatively benign ash chemistry and meet environmental standards for sulfur and nitrogen oxide emissions. In addition, it must be relatively easy to grind and to handle.

The requirements of coals purchased for coke making are much different from those used in other processes. Only a certain class of coals possessing very specific properties and composition are suitable for the making of a quality coke for blast furnace use. In what follows, these differences will be discussed from the point of view of coal formation, characterization and classification in context with their use in the various steel making operations.

Coal is a readily combustible rock containing more than 50% by weight or more than 70% by volume of carbonaceous material including inherent moisture. It is formed from the compaction and induration of various altered plant remains similar to those found in peat. Peat consists of plant debris that, for the most part, was accumulated in place in swamps, marshes or bog environments from the different parts of living plants, their roots, stems, leaf materials and reproductive parts. At a more basic level, plants are composed of various membranes and substances that are chemically distinct. Some of the more important ones are carbohydrates (starch, cellulose, lignin), protoplasm, chlorophyll, oils, seed coats, pigments, cuticles, spores and pollen, waxes and resins. In addition, degradation products, bacteria, fungi, invertebrate and vertebrate organism also may contribute to the organic fraction of a peat. Because of the depositional environment, inorganic components can be deposited with the accumulating organic debris or may form in place by chemical reactions or be fixed by bacteria or the plants themselves. Consequently, peat is composed of water, carbon, hydrogen, oxygen, nitrogen, sulfur, mineral matter, trace elements and contains the building blocks for coal formation.

For the most part, coals that are utilized today were deposited as peat many hundreds of millions of years ago from plants that are now extinct or that represent an insignificant part of today’s flora. However, the processes of accumulation and preservation of such a wide variety of organic materials have changed little over geologic time. The environmental setting requires that there be high organic productivity and slow continuous subsidence that insures that the peat is protected from inundation by inorganic sediments or from becoming dry and exposed to oxidation. Studies of modern peat-forming environments show a succession of plant communities exist in any given place that varies with time vertically and laterally depending upon local conditions. These different communities, including aquatic plants, reeds, sedges, forests and mosses, contribute variable amounts and types of organic matter to the peat. The processes that influence changes in plant communities and the plants themselves account for the heterogeneous chemical and physical properties of the resulting coal.

Following deposition and in the early stages of burial, plant remains undergo biochemical coalification principally from the action of bacteria and fungi. This process of humification largely alters the chemical nature of the organic materials and may continue for sometime after burial, but ultimately gives way to factors involved in geochemical coalification. This stage of coal development is controlled primarily by the rise of temperature in response to the geothermal gradient as organic material becomes buried at greater depths, the time over which this process occurs and the pressures to which it is subjected. Thus, the types of plants and plant tissues contributing to the original organic deposit and the action of biological and geologic events during and after burial are responsible for the great diversity of the resource we refer to as coal.

the largest single use of coal, fuel for the blast furnace, the production of metallurgical coke, injection with the hot blast, steam and electricity, direct smelting of iron processes, a readily combustible rock, carbonaceous material, inherent moisture, peat, bog environments, degradation products, bacteria, fungi, invertebrate and vertebrate organism, geochemical coalification.

прискорити реакції, нагрівання полум’ям, об’єднувати з, розплавлений метал, вимагається (потрібно), горн, замість, енергетичні вимоги, процес очищення, залізо в чушках, залізняк (залізна руда), сталева труба, кисень високої чистоти.